Understanding the Prebid Server Response Correction Module: Practical Insights for Publishers

Publishers running header bidding with Prebid Server often face headaches when bidders return non-standard creatives—especially in mobile app environments. One persistent issue is video demand partners sending HTML creatives instead of VAST, disrupting ad delivery and revenue.

The Response Correction module in Prebid Server provides a practical solution for these situations. Let’s dive into what this module is, why it’s needed, and how to configure it for smooth, error-free monetization.

What Is the Prebid Server Response Correction Module?

Prebid Server processes bid responses from a wide range of demand partners, each interpreting specs slightly differently. The Response Correction module is a toolkit designed to catch and fix certain common mistakes in these responses before they negatively impact your monetization stack or break your ad flows. In its current form, it specifically addresses bidders who claim to be returning a video ad, but provide HTML instead of VAST—a scenario that frequently causes operational complexity for publishers.

Why HTML Creatives for Video Are a Problem

Most mobile app ad servers and SDKs expect video responses to be VAST XML. If a bidder declares a video format but submits HTML, ad servers like Google Ad Manager (GAM) may not render the creative, leading to wasted impressions and troubleshooting headaches. To work around this, publishers often create extra GAM line items or exclusionary rules, which isn’t scalable or elegant.

The Response Correction module tackles this by automatically reclassifying the problematic bid as a banner, aligning the response with what the ad server can actually deliver.

How the App Video HTML Correction Works

The ‘app-video-html’ correction selectively inspects bid responses for app environments. It determines whether incoming bids labeled as video actually contain valid VAST, and if not, it takes corrective action to prevent delivery errors downstream.

Bid Response Processing Flow

Here’s how the correction operates on each bid:

– If the bid is from a non-excluded bidder and indicates a video type, the module checks the ad markup for VAST XML.
– If VAST is found, the bid passes through.
– If no ad markup is present or the markup is native (e.g., JSON with ‘assets’), the bid is ignored but logged for review.
– If the markup is neither VAST nor native, the system re-classifies the bid as a banner, updates the response metadata, and logs a warning (at a sampled rate to avoid log noise).

This ensures that your server and ad delivery endpoints receive properly classified bids and don’t attempt to serve creatives they can’t handle.

Example: Header Bidding in a Mobile App

Consider a scenario where two bidders return video bids to your mobile app placement. Bidder A sends VAST XML as expected, but Bidder B returns an HTML snippet. Before the Response Correction module, GAM rejects Bidder B’s creative, causing wasted demand. With the module enabled, Bidder B’s response is instantly switched to a banner, avoiding fill failures and making troubleshooting much easier.

Configuration Strategies and Best Practices

Enabling the Response Correction module is straightforward but must be handled with care, especially when integrated with existing ad server line items and rules.

Setting Up the Module

Configuration is managed per account, meaning you can enable or disable the module—and its specific corrections—at a granular level. Key settings include:
– ‘enabled’: Turns the module on or off.
– ‘app-video-html.enabled’: Activates the video HTML correction feature.
– ‘app-video-html.excludedbidders’: Allows you to exempt specific bidders from the correction if needed.

A typical config will look like this (paraphrased):

– Activate the response correction module for your PBS account.
– Enable app-video-html correction.
– List any bidders you trust or who already comply with standards in the excludedbidders array.

For sensitive accounts, consider rolling out the correction first on test or lower-traffic placements to ensure it doesn’t disrupt delivery.

Timing Corrections with Ad Server Changes

It’s vital to coordinate any correction with your ad server setup. If Prebid Server begins reclassifying video as banner while GAM line items still expect video, you’ll see delivery failures. Plan a synchronized update—first to the module, then to GAM line items and targeting. This alignment avoids downtime and preserves your fill rate.

What this means for publishers

For publishers, the Response Correction module reduces operational friction, especially in app video environments. It offers a safeguard against demand partners who send incompatible creatives, resulting in fewer workflow hacks—like creating redundant GAM line items—while maximizing usable demand and minimizing ad delivery errors. Ultimately, this means fewer lost impressions, faster troubleshooting, and more reliable revenue streams.

Practical takeaway

Every publisher relying on header bidding in mobile apps should review the Response Correction module, particularly if they’ve encountered issues with non-VAST video creatives. Start by auditing your app demand partners for compliance—then enable the module with a controlled rollout, monitoring for improvements or unintended impacts.

Make sure your ad server line items, targeting criteria, and Prebid Server configuration stay in sync. Keep a close watch on logs for unexpected behaviors, especially if you allow some bidders as exceptions. With careful implementation, the Response Correction module can streamline ops, reduce errors, and ultimately lift monetization quality.